POST null because property type does not match? - asp.net-core

Question

I have a asp .net core API with simple REST methods like this:
[Route("api/[controller]")]
public class SomeController : ControllerBase
{
[HttpPost]
public async Task<IActionResult> Insert([FromBody] ItemClass newItem)
{
[...]
return Ok();
}
}
The model class is pretty simple as well:
public class ItemClass
{
public string Id { get; set; }
public string Name { get; set; }
public string Description { get; set; }
public bool IsActive { get; set; }
}
When I POST this JSON to the service
{
"id": null,
"name": "Some name",
"description": "Some description",
"isActive": null
}
the method is called with newItem set to null. No error, no exception, the the object was just null. It took me quite a while to figure out the parameter isActive was the cause of the problem. In the class I defined it as bool, but JSON defined it as null. When I either change the value to true or false or when I leave it out completely or when I change the parameter to bool? it works again. The object is deserialized correctly.
I'm used to asp net core APIs to be very resilient. Usually when a parameter is simply set to its default when it can not be parsed correctly from the message.
But why does the whole object become null here?
Is there at least a way to tell asp net core to throw an exception when the deserialization fails?

Answer 1

When null is mapped to the bool, resulting in a type mismatch exception, it will cause the whole object become null.
If this api is 3.x, it will trigger 400. But in 2.x and 5.0, they have no exception. You can handle the null value through NewtonSoft.json.
A simple way to handel it with this configuration, it can assign a default value to bool, but it doesn't trigger exception.
In 2.x
services.AddMvc()
.AddJsonOptions(options=>
{
options.SerializerSettings.NullValueHandling = Newtonsoft.Json.NullValueHandling.Ignore;
});
5.0
services.AddControllers()
.AddNewtonsoftJson(option=>
{
option.SerializerSettings.NullValueHandling = Newtonsoft.Json.NullValueHandling.Ignore;
});
If must return an error, you have to use a custom model binding.
public class CustomBindClassBinder : IModelBinder
{
public Task BindModelAsync(ModelBindingContext bindingContext)
{
var itemClass = new ItemClass();
using (var reader = new StreamReader(bindingContext.HttpContext.Request.Body))
{
var body = reader.ReadToEndAsync();
var mydata = JsonConvert.DeserializeObject<JObject>(body.Result);
if(mydata["isActive"].ToString()==""|| mydata["isActive"].ToString() == null)
{
bindingContext.Result= ModelBindingResult.Failed();
throw new Exception("isActive is not correct");
}
else
{
itemClass.Id = mydata["id"].ToString();
itemClass.Name = mydata["name"].ToString();
itemClass.Description = mydata["description"].ToString();
itemClass.IsActive = bool.Parse(mydata["isActive"].ToString());
bindingContext.Result = ModelBindingResult.Success(itemClass);
}
}
return Task.CompletedTask;
}
}
In action
[HttpPost]
public async Task<IActionResult> Insert([FromBody][ModelBinder(typeof(CustomBindClassBinder))] ItemClass newItem)
{
return Ok(newItem);
}